A conventional fabrication (patterning) technique is known in which a sidewall spacer is formed on a side surfaces of a dummy pattern which is called a core, and after removing the core, a microscopic pattern is formed on a semiconductor substrate using the sidewall spacer as an etching mask. Since a width of the mask composed of the sidewall spacer is determined by a deposited thickness of a material film of the mask before shaped into a sidewall shape or by etching time during the shaping, more accurate dimension control, including line width control, is possible than by conventional lithography. Thanks to this method, it is possible to reduce variation of mask dimension compared to a broadly used etching hard mask formation method using a combination of a resist coating and lithographic exposure. This technique, for example, is disclosed in a non-patent literary document of A. Kaneko et al., IEDM Tech. Dig. pp. 863-866, 2005.
However, since the sidewall spacer mask has a ring pattern surrounding a periphery of the core due to formation method thereof, it is necessary to trim the sidewall spacer mask to shape the ring pattern into a line-and-space pattern by applying additional lithography process and an etching process again using a mask called a pattern cut mask or a trimming mask in order to use the sidewall spacer mask as a mask for forming a linear pattern called line-and-space on the workpiece material.
Specifically, when a fin of an SRAM cell, or another type of memory cell such as DRAM, composed of FinFET is formed applying a line-and-space pattern, a mask having in a critical design level having a submicroscopic pattern must be used as a patterning photomask for core formation and a trimming photomask for a sidewall spacer mask. Therefore, the production cost of the entire chip including cost of the mask becomes high. In addition, for a photolithography process using these photomasks, it is necessary to use a lithography technique (e.g., immersion lithography, etc.) which is good at controllability of dimension or overlay accuracy but is highly difficult and at high cost.